Alpha-Tritium isotope effect studies of pyruvate carboxylase and oxalacetate transcarboxylase indicate that an electrophilic displacement rather than a stepwise carbanion mechanism may be occurring. These studies will be extended by varying conditions and using model electrophilic reactions such as organo-metallic cleavage to interpret the invervse Alpha-T effect. BIBLIOGRAPHIC REFERENCES: Rose, Irwin A. Mechanism of the aldose-ketose isomerase reactions. Advances in Enzymology, Vol. 43, ed. A. Meister, Wiley and Sons, 1975. Creighton, Donald J. and Rose, Irwin A. Oxalacetate decarboxylase activity in muscle is due to pyruvate kinase. J. Biol. Chem. (in press).